Packing-density calculation of thin fluoride films from infrared transmission spectra

Optical thin films of MgF(2) and NdF(3) have been made by molecular-beam deposition in ultrahigh vacuum. The film packing density was calculated from the water amount that filled the cavities of the films in air. For that the transmission in the IR spectral region with a characteristic water absorption band at a wave number of 3400 cm(-1) was measured. The influence on the packing density of a modification of thin-film morphology by stratification of very thin sublayers of different crystallizing fluorides is tested.     

Retrieval of optical constants and thickness of thin films from transmission spectra

We discuss a new method to estimate the absorption coefficient, the index of refraction, and the thickness of thin films using optical transmission data only. To solve the problem we used a pointwise constrained optimization approach, defining a nonlinear programming problem, the unknowns of which are the coefficients to be estimated, with linear constraints that represent prior knowledge about the physical solution. The method applies to all kinds of transmission spectra and does not rely on the existence of fringe patterns or transparency. Results on amorphous semiconductor thin films and gedanken films are reported. They show that the new method is highly reliable.     

Improved method for determination of optical constants of organic thin films from reflection and transmission measurements

A new technique for determining the optical properties of organic thin films is presented. A detailed evaluation of the accuracy of the determined optical constants has been performed, and the best combination of measured values yielding the smallest errors in the index of refraction for realistic experimental uncertainties has been found. The proposed method utilizes the fact that optical constants are smooth continuous functions, which reduces the possibility of encountering multiple solutions. The method consists of two steps. In the first step the optical constants at all wavelengths and the film thickness are determined. In the second step the thickness and the imaginary part of the index of refraction are kept fixed while we reevaluate the real part of the index of refraction by using a different objective function with improved sensitivity to the refractive index. After verifying that the proposed method is capable of an accurate estimation of optical constants, we determine the index of refraction data of vanadyl-phthalocyanine in the visible spectral range.     

Determination of thickness, refractive index, and thickness irregularity for semiconductor thin films from transmission spectra

A simplified theoretical model has been proposed to predict optical parameters such as thickness, thickness irregularity, refractive index, and extinction coefficient from transmission spectra. The proposed formula has been solved for thickness and thickness irregularity in the transparent region, and then the refractive index is calculated for the entire spectral region by use of the interference fringes order. The extinction coefficient is then calculated with the exact formula in the transparent region, and an appropriate model for the refractive index is used to solve for the extinction coefficient in the absorption region (where the interference fringes disappear). The proposed model is tested with the theoretical predicted data as well as experimental data. The calculation shows that the approximations used for solving a multiparameter nonlinear equation result in no significant errors.     

ZnO薄膜材料的发光谱

随着人们对ZnO薄膜材料发光特性的不同深入，发现了不同能量位置的多个发光峰，本文对用不同方法制备的ZnO薄膜材料的发光谱、发光特性及其相应的发光机制、国内外研究动态进行了综合评述。介绍了由带间跃迁、激子复合和缺陷能级引起的发光和发光谱特性。     

Electroreflectance spectra of thin silicon films

Electroreflectance spectra for thin silicon films have been investigated in the photon energy region 2.8–5.0 eV. The critical point energy E₁(E′'₀) and the broadening parameter Γ were determined for unexposed and ion-bombarded surfaces. Definite correlation between Γ^-1 and the Hall mobility was found. It is concluded that the variations in E₁(E_'0) for the films are caused by the emergence of density “tails” and the existence of inward mechanical microtensions.     

Transmission and reflection ellipsometry of thin films and multilayer systems

Ellipsometric studies are generally carried out in the reflection mode rather than in the transmission mode, requiring invariably opaque substrates or substrates in which the backreflection is minimized or suppressed by different methods. In the present research we used a transmission and reflection photoellipsometry method to study electrochromic materials and their multilayer systems deposited on thick substrates. The role of the substrate is examined carefully, and the contributions from multiple reflections in the substrate are taken into account in the theoretical treatment. This procedure not only allows the study of thin films deposited on quasi-transparent substrates, but when carried out in conjunction with reflection measurements it greatly improves the accuracy in the determination of the optical constants. Optical measurements are carried out on an automatic reflection transmission spectroscopic ellipsometer. Solid-state ionic materials used in electrochromic systems such as indium tin oxide, tungsten oxide, and their multilayer structures deposited on glass substrates are used as examples. A software based on the above theory, optikan, was developed to model and analyze such systems. It is demonstrated that the photoellipsometry method proposed is especially suited to analyzing electrochromic materials and transmitting devices in a nondestructive way.     

Diffuse reflection of ceramics coated with dielectric thin films

We have studied the diffuse reflection properties of ceramics in the presence of dielectric thin films on the surface. A simple optical model was proposed in which interference effects in a thin film were considered for light scattered out of a ceramic in various directions. Measurements were performed on angle-resolved reflection spectra of a thin-film-coated alumina ceramic in the case of normal incidence. They showed that the presence of the thin film on the ceramic's surface modified the angular distributions of scattered radiation from that of a bare ceramic, which suggested a way to tailor the scattering properties of a diffuse reflector as needed.     

Dielectric modeling of transmittance spectra of thin ZnO:Al films

A dielectric model comprising band gap transitions and free electron excitations (Drude model) is successfully applied to simulate transmittance spectra of ZnO films doped with 0.5%, 1% and 2% Al. The Drude formula contains a frequency-dependent damping term in order to get a good fit in the visible spectral region. Useful physical parameters obtained from the fit are electron density and mobility within the grains, film thickness, band gap and refractive index. The optically determined film thickness agrees with that obtained with the stylus method within 2%. The optically determined electronic parameters are compared with those obtained by electrical measurements. Contrary to thin In₂O₃:Sn films, the Drude mobility inside the grains is similar to the direct current Hall mobility indicating more perfect film growth without forming pronounced grain boundaries. Maximum value is 35 cm²/V s. The effective electron mass is estimated to be about 0.6 of the free electron mass. The refractive index at 550 nm decreases with increasing electron density.     

Near-infrared reflection from periodically aluminium-doped zinc oxide thin films

Multilayers of aluminium-doped zinc oxide (Al:ZnO) as a heat-reflection material were prepared by a reactive sputtering method with intermittent Al doping or Al content modulation. A drop in the refractive indices n around the plasma wavelength λ_p of 1456 nm for the optimally-doped Al:ZnO layers formed the periodic distribution of n in the multilayers. The periodic n provided selective reflection of approximately 60% under λ_p and shielded near-infrared solar radiation containing high energy, which was impossible to be reflected from the Al:ZnO monolayer. The selective reflection was accompanied by infrared reflection above λ_p, low emissivity and no subsequent visible reflection, which allowed the multilayers to achieve compatibility between the solar heat gain coefficient of 0.6 and the visible transmittance of nearly 80%.     

氢化非晶硅薄膜的红外光谱分析和桥键氢扩散假设

通过红外透射光谱研究了在光诱寻退火中退火条件对氢化非晶硅薄膜的结构和光电特性的影响,实验所用样品采用热丝辅助微波电子回旋共振化学气相沉积方法制备。我们用桥键氢扩散模型来解释退火中的不同现象。样品的红外光谱在630和2000cm^-1处的吸收系数有所增加,说明了原先的成键氢发生了移动和溢出,我们认为通过光诱导产生栽流子的非辐射复合以及桥键氢和深俘获氢原子的交换,产生了大量的桥键氢原子,它们相互结合形成分子氢,氢溢出要优于氢团聚。     

Simple expressions for Bragg reflection from axially excited chiral sculptured thin films

Reported here is the derivation of analytic expressions for the reflection coeffcients of a halfspace filled by a chiral sculptured thin film (STF) that is axially excited by a normally incident plane wave at the centrewavelength of the Bragg regime. Although these expressions are correct to the second order with respect to a small parameter that delineates the local anisotropy of the chiral STF, their first-order reductions are particularly simple and very adequate for practical purposes. A small difference between the two cross-polarized reflection coeffcients has also been found. The results are explained on the basis of a simple model which utilizes the standard Fresnel equations for a scalar dielectric halfspace, combined with coupled wave theory.     

Enhanced photoluminescence spectroscopy for thin films using the attenuated total reflection method

We present a powerful spectral photoluminescence measurement method for thin films that utilizes the enhanced absorption of the fluorescent thin films on metal thin films with attenuated total reflection (ATR). The photoluminescence measurement has the advantageous effects of avoiding transmitted light and preventing the loss of luminescence through waveguiding in the film substrates. The ATR modes excited by low-power incident light provide fluorescence intensities that are considerably larger than that of conventional photoluminescence measurements and preserve the spectral profile of the photoluminescence.     

X-ray photoelectron and auger electron spectra of magnesium thin films

In order to study the epitaxy of gold on KBr (100) surfaces, the degree of epitaxial order was measured and its dependence on the experimental parameters evaporation time, flux rate and substrate temperature was determined. The specimens were produced in UHV, fixed in situ, and examined under an electron microscope. The micrigraphs taken in the electron microscope were analysed quantitatively with an electronic image analysing computer, the area covered, the cluster density and the cluster size distribution being investigated. The results confirm a theory which differentiates between spontaneous orientation and cluster alignment.     

Computational design of solar reflection and far-infrared transmission films for a variable emittance device

A smart radiation device (SRD) that is a variable emittance radiator has been studied as a method of thermal control for spacecraft. The SRD consists of manganese oxide with a perovskite-type structure, and the total hemispherical emittance of the SRD changes considerably depending on temperature. Here we propose an optimal method of designing multilayer films for the SRD by using agenetic algorithm. The multilayer films reflect solar radiation and transmit far-infrared radiation to maintain variation of the infrared optical properties of the SRD.     

Lattice distortion energy spectra of thin evaporated silver films

Thin silver films (thickness, 12.5–160 nm) were evaporated under ultrahigh vacuum conditions onto clean glass substrates (substrate temperature, 225 K). During the growth process a large number of lattice defects were incorporated (condensation rate, 0.2 and 0.01 nm s^-1). The films were subjected to heat treatment (constant heating rate, 0.1 K s^-1) and the variation in the electrical resistance was measured as a function of temperature. Using Vand's theory the initial lattice distortion energy spectra of the films were determined from the resistance-temperature data. The lattice distortion energy function has maximum values. While the number of distortions with a decay energy of about 0.8 eV increases rapidly with decreasing film thickness, the number of distortions with a decay energy of about 0.93 eV varies only slightly.     

Grating-coupler assisted infrared reflection absorption spectroscopy for the characterization of organic thin films

We demonstrate how grating-coupler assisted infrared reflection absorption spectroscopy can be used to simultaneously determine the chemical identity and relative thickness of organic thin films. With a grating substrate, a threshold anomaly associated with passing off of the -1 diffracted order occurs at grazing angles of incidence, resulting in a sharp absorbance in the infrared. The position of this peak is sensitive to the grating geometry as well as the dielectric environment near its surface. Thus, shifts in the peak position can be used to determine the relative thickness of adsorbed films or quantify molecular adsorption events. To illustrate the characteristics and sensitivity of this phenomenon, several samples were prepared and tested, including self-assembled alkanethiolate monolayers with 11-mercaptoundecanoic acid, 11-mercapto-1-undecanol, decanethiol, and a covalently linked layer of bovine serum albumin on a commercial, gold-coated grating. For these samples, the position of the threshold absorbance peak shifted to lower wavenumbers as film thickness increased, which is consistent with calculated shifts based upon an increasing refractive index at the interface. The sensitivity of this shift was measured to be 3.7 cm(-1) nm(-1). These results illustrate how a grating substrate can be exploited in a standard infrared reflectance measurement to provide additional information about the relative thickness of adsorbed surface films.     

Modeling inhomogeneous materials with preset spectra of reflection and transmission of electromagnetic waves

Materials with inhomogeneous in-depth profiles, which possess preset spectra of reflection and transmission of electromagnetic waves, have been modeled using the Galerkin and Levenberg-Marquardt methods. A solution of the inverse problem is used to determine inhomogeneous dielectric permittivities of the material layers. It is demonstrated that both transparent and absorbing materials can be modeled with good precision.